Do you have a previous eviction history? Additional applications: If you require a guarantor or cosigner, they should also submit an application.This form is for the Co-Signer application. Once the application is complete, your information will be submitted for a credit check. We are delighted to have you join our community, First Site is the ultimate home for Illinois State students. A cosigner for an apartment takes on the financial responsibility for a lease. Learn how having a cosigner can help someone get approved for an apartment. Every person that will occupy the apartment must fill out a separate Application except if they are under the age of 18. The co-signer application is to be completed with the co-signers' information, including social security number and salary amount. This includes the responsibility to pay rent and follow the lease agreement closely.